Shifting into the information age, a demand for finer and larger display screen has not been higher for a display device of AV equipment such as television and of OA equipment such as a monitor. In order to meet such a demand, development and practical application of larger screen has been under way in various display devices such as CRT (Cathode Ray Tube) display device, liquid crystal display device (LCD: Liquid Crystal Display), plasma display device (PDP), EL (Electro Luminescent) display device, and LED (Light Emitting Diode) display device.
Of those devices, compared with other display devices, the liquid crystal display device has such an advantage in that the dimension of the depth (thickness) can be made significantly thinner, power consumption is low, and a full-color image can be obtained with ease. For these reasons, the liquid crystal display device has been applied in a wide variety of fields, and expectations are high for realizing a larger screen.
However, the liquid crystal display device has a drawback that when the screen is made larger and the resolution is increased, the fraction defective induced by breakage of signal lines and a pixel failure is conspicuously increased in the manufacturing process of a liquid crystal panel, which is a component of the liquid crystal display device, and this increases the cost of the device.
In order to solve this problem, for example, Japanese Publication for Unexamined Utility Model No. 191029/1985 (Jitsukaisho 60-191029) discloses a liquid crystal panel having a structure wherein, as shown in FIG. 12, one of a pair of electrode substrates 101 and 102 (here 101) sandwitching a liquid crystal layer 104 constitutes a single multi-substrate 101 composed of a plurality of small substrates 101a which are connected to one another on the sides by an adhesive 103. In FIG. 12, 105 is a sealant for combining the multi-substrate 101 and the electrode substrate 102.
Also, Japanese Publication for Unexamined Utility Model No. 11187/1986 (Jitsukaisho 61-11187) discloses a structure wherein, in addition to the arrangement wherein the plurality of small substrates 101a constitute the multi-substrate 101 by being connected to one another on the sides, as shown in FIG. 13, the plurality of small substrates 101a are positioned side by side close to one another, and are connected to one another by attaching a resin sheet 106 covering the surfaces of the small substrates 101a.
Further, Japanese Unexamined Patent publication No. 122769/1996 (Tokukaihei 8-122769) discloses a structure wherein a plurality of liquid crystal panels are placed side by side on a transparent supporting substrate, and a single multi-panel is composed by combining (a) the plurality of liquid crystal panels with each other and (b) the supporting substrate and each of the plurality of liquid crystal panels.
In the case where the multi-substrate 101 or the multi-panel is composed by connecting the plurality of substrates or the liquid crystal panels to one another, when diffraction or scattering of light occurs at the connected portion, the connected portion becomes noticeable and the display quality is lowered. Thus, as the adhesive 103, a material, such as UV curable adhesive, having adhesion and substantially the same refractive index as that of the small substrates 101a or the electrode substrates constituting the liquid crystal panel is adopted.
As an example of the multi-panel structure as described above, although not shown, a display device disclosed in Japanese Unexamined Patent publication No. 271871/1996 (Tokukaihei 8-271871) is available. This display device has a structure wherein the multi-panel is sandwitched between a large substrate and a coating layer made from polymers or glass.
However, in the structure of Japanese Publication for Unexamined Utility Model No. 191029/1985 (Jitsukaisho 60-191029), as shown in FIG. 12, it is required to treat the adhesive 103a which has protruded on the back side of the multi-panel 101. When the protruded adhesive 103a is scraped off after curing, a step-difference or uneven surface is generated on the scraped portion and scattering of light is induced, and the connected portion becomes noticeable. On the other hand, when the adhesive 103a is left exposed, the surface of the adhesive 103a is scratched in the manufacturing process, and scattering of light is also induced this time by the scratch, and as a result the connected portion becomes noticeable and the display quality is lowered.
Meanwhile, in the structure of Japanese Publication for Unexamined Utility Model No. 11187/1986 (Jitsukaisho 61-11187), although it is not required to treat the adhesive 103a, it is difficult to ensure that the small substrates 101a are connected close to one another on the sides, and a layer of air is formed at the connected portion. As a result, there is a case where the connected portion becomes noticeable due to the difference in refractive index of the air layer and the substrates.
Further, Japanese Publication for Unexamined Utility Model No. 11187/1986 (Jitsukaisho 61-11187) does not disclose the manufacturing steps, and as shown in FIG. 14(a), when the multi-substrate 101 is composed by connecting the small substrates 101a to one another by the resin sheet 106, and the multi-substrate 101 is combined with the electrode substrate 102 by the sealant 105 provided on the periphery of the electrode substrate 102, as shown in FIG. 14(b), a non-uniform cell gap (thickness of liquid crystal layer 104) is induced by the nonuniformity in the substrate thickness of the small substrates 101a made of glass or other materials, and the display quality is significantly lowered.
Also, when the cell gap is to be made uniform by combining first the electrode substrate 102 with each of the small substrates 101a by the sealant 105, as shown in FIG. 15, a step-difference is generated by the thicknesses of the substrates. As a result, an air bubble 107 is likely to be trapped at the portion of the step-difference when attaching the resin sheet 106.
In the structure of Japanese Unexamined Patent publication No. 122769/1996 (Tokukaihei 8-122769), the adhesive protrudes on the surface (other side of the surface facing the supporting substrate) of the multi-panel, thus having the same problem as that of Japanese Publication for Unexamined Utility Model No. 191029/1985 (Jitsukaisho 60-191029).
Also, in Japanese Unexamined Patent publication No. 271871/1996 (Tokukaihei 8-271871), the main object is to prevent volume shrinkage of the adhesive filling a spacing between a large substrate and a multi-panel so as to stabilize the structure of the multi-panel. For this reason, the protrusion of adhesive from the connected portion of the panels to the side of the coating layer cannot be prevented effectively, and the disclosure is applicable only to the multi-panel structure.